This is a mortar and pestle dating to 1750 CE, used by the Ohlone people. They used this to ground acorns (not this one) into a coarse powder. The powdered acorns, their major plant diet, was soaked in water to remove their natural bitterness. After that they cooked it into a gruel, made cakes and then baked them in an oven
Cooking acorns in 1750 CE
Published
Still in some villages people have this with them.